Related Field
The present invention relates to a magnetic transmission for a conveyor drive unit used to drive a conveyor belt or a conveyor chain in a conveyor system.
Description of Related Art
Conveying devices, such as those which are used for moving objects between different stations in e.g. a factory or a production plant, usually comprise a conveying track in the form of a belt or a chain. The conveying tracks can be recessed in a trench with vertical side surfaces. Alternatively, they can be located on the horizontal upper surfaces of the trench or beam or may be arranged in some other way. The objects to be conveyed are arranged slidably in relation to the conveying tracks, either directly or via supporting means. Larger objects are often conveyed on supporting means also known as pallets, and smaller objects may be conveyed using a small carrier often referred to as a carrier puck.
The conveyor chain is forwarded by a drive unit comprising a motor. The conveyor chains runs in conveyor beams and glides on slide rails attached to the conveyor beams. Both the conveyor chain and the slide rails may be made from a low friction material in order to reduce power consumption, to reduce wear and to reduce noise caused by vibrations. In the forward direction, i.e. when the chain transports objects, the underside of the upper body bears on upper slide rails of the conveyor beam. In the return direction, i.e. when the chain travels upside down in the return path, the upper side of the conveyor chain may be supported by a bearing surface on which the conveyor chain glides. The conveyor chain may also be provided with tabs or protrusions by which the chain may bear on an inner slide rail of the conveyor beam.
The drive unit is often positioned at an end of the conveyor, where the chain changes direction from a forward direction to a return direction at the bottom of the conveyor beam. It is also possible to arrange drive units as intermediate drive units, placed along the conveyor. A horizontal bend drive unit is used where an endless chain does not have a return chain. Other types of drive units are also possible to use. Also conveyor belts are driven by a drive unit arranged at one end of the conveyor.
The most common drive unit is a drive unit positioned at one end of a conveyor. Such a drive unit comprises a motor, often a gear and a relatively large drive wheel which is provided with notches along the circumference of the drive wheel, when the drive wheel is to drive a conveyor chain. The notches are semi-circular and will engage with drive protrusions of the conveyor chain in order to drive the conveyor chain forwards. A conveyor belt having a toothed inner side will also use a drive wheel having grooves or teeth that will interact with the toothed inner side. A smooth conveyor belt will preferably be driven by a drive wheel having a smooth but rough surface in order to increase the friction between the drive wheel and the drive belt. The drive surface may also be treated with a friction increasing treatment, such as a coating of rubber or plastic.
The drive unit is normally a relatively large motor comprising a transmission and preferably a friction clutch in order to allow for slippage if e.g. a product is caught or the conveyor chain is stopped for some other reason. The motor, the transmission and the clutch are normally arranged at the side of the conveyor track. The transmission will convert the relatively high rotational speed of the electric engine to a relatively low rotational speed of the drive wheel. At the same time, the torque of the drive wheel is increased compared to the electric motor.
Other types of drive units for a conveyor chain are also known, with various solutions using drive belts with different engaging means to engage the conveyor chain.
GB 2472020 A discloses a drum motor comprising a radially mounted drive element comprising an electrical machine with integral magnetic gearing. The motor has an outer fixed stator housing provided with a wound stator with permanent magnets surrounding a high speed low torque permanent magnet rotor and a low speed, high torque rotor comprising magnetic pole pieces being arranged between the stator and the high speed rotor and being connected to an output drive shaft. The low speed rotor is connected to an input shaft. The outer stator housing is fixed.
WO 2015/121647 A discloses a system comprising a pole piece rotor, a permanent magnetic rotor and a fixed outer stator.
US 2012/0146442 A discloses an electrical machine having an inner rotor with permanent magnets, an outer rotor having a plurality of pole-pieces that enable the magnetic interaction between the pluralities of permanent magnets, and an outer stator that is fixed.
There is room for an improved drive unit for an endless conveyor chain comprising a plurality of chain links.